Hwarim Im

Effects of defect creation on bidirectional behavior with hump characteristics of InGaZnO TFTs under bias and thermal stress

We investigated the hump characteristics of amorphous indium–gallium–zinc oxide thin-film transistors. The device showed a field effect mobility of 24.3 cm2 V−1 s−1, a threshold voltage (Vth) of 4.8 V, and a subthreshold swing of 120 mV/dec. Under positive gate bias stress, Vth showed bidirectional shift with a hump. Vth was positively and negatively shifted in the above-threshold and subthreshold regions, respectively. At high temperatures, Vth was more positively shifted without bidirectional shift. Under simultaneous drain bias stress (VDS,stress), the hump was maintained. However, the bidirectional shift was not observed with an increasing VDS,stress. The hump and positive shift are related to the defect creation of the shallow donor-like and deep-level acceptor-like states, respectively. We performed a two-dimensional device simulation to further investigate this phenomenon. By varying the peak values of the Gaussian shallow donor-like and deep acceptor-like states, we qualitatively confirmed the relationship between the two states and transfer curve changes.

Effects of the defect creation on the bidirectional shift of threshold voltage with hump characteristics of InGaZnO TFTs under bias and thermal stress

We have investigated the hump characteristics of amorphous indium gallium zinc oxide (a-IGZO) thin film transistors (TFTs). Under positive gate bias stress, the threshold voltage (Vth) of a-IGZO TFTs showed bidirectional shift with hump; the positive shift in above Vth region and negative shift in subthreshold region. The amount of bidirectional shift depended on the temperature or drain voltage of stress condition. It was concluded that the origins of the bidirectional shift with hump were the shallow donor-like states and deep-level states creation in the semiconductor bulk or at the semiconductor/dielectric interface. Two-dimensional device simulation was also performed to further investigate this phenomenon.

Accurate Defect Density-of-State Extraction Based on Back-Channel Surface Potential Measurement for Solution-Processed Metal-Oxide Thin-Film Transistors

We report more accurate extraction method of the defect density of states for solution-processed indium-gallium-zinc-oxide (IGZO) thin-film transistors (TFTs). Since the solution-processed IGZO TFTs have a very thin (~8 nm) active semiconductor layer, their back-channel surface potential should be considered in the field-effect method. If the back-channel surface potential is ignored, deviation between theoretically derived and experimentally measured activation energy data becomes more significant as the thickness of the semiconductor layer decreases in comparison with its Debye length. Dependence of the back-channel surface potential on the applied gate voltages was verified by scanning Kelvin probe microscopy and found to be proportional to the gate voltages. The modified field-effect method provided a more accurate model of the activation energy over the subthreshold region and correspondingly more accurate defect density of states of the IGZO TFTs.

Solution-processed high-k dielectrics for low-voltage IGZO TFTs

There have been many efforts in reducing the operating voltage of thin-film transistors (TFTs) by using dielectric materials with high capacitances, such as high-k inorganic dielectrics, organic/inorganic hybrid dielectrics, and self-assembled nanodielectrics [1]. Aluminum oxide (Al2O3) and zirconium oxide (ZrO2) are the representative high-k dielectric materials due to its good leakage properties from its high bandgap, high permittivity, and solution process compatibility. Using solution-based materials, simple fabrication processes, such as spin-coating, inkjet-printing, and roll-to-roll process have been extensively attempted to make electronic devices and circuits with low-cost fabrication possibilities and large-area fabrication compatibilities [2]. In this study, we report the fabrication of solution-processed indium-gallium-zinc-oxide (IGZO) TFTs which operated in low voltage regime below 5 V and their electrical characteristics.

The effects of annealing process under H 2 /N 2 environment on the characteristics of low temperature solution processed InGaZnO thin film transistors

We demonstrated solution processed InGaZnO (IGZO) TFTs annealed at low temperature under H₂/N₂ environment and investigated the effects of annealing process under H₂/N₂ environment on the characteristics of low temperature solution processed InGaZnO TFTs.